The concept of polymerizing phenols, e.g., 2,6-xylenol, in a self-precipitating system was first noted by Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875. The products of the process are thermoplastic resins known as polyphenylene oxides (or polyphenylene ethers). Later workers reported work with self-precipitating systems, e.g., Belgian Pat. No. 776,044 and German Patent Publication No. P 21 26 434.6. The catalyst systems used in the foregoing work, in general, comprised CuCl with either N,N-dimethylamine, N-ethylamine, N,N-diethylamine; manganese bis(salicyaldehyde)-ethylenediamine with an ancillary amine or an alkali base; CuSO.sub.4 with pyridine or cobalt bis(salicylaldehyde)ethylenediimine with pyridine.
Among the catalysts proposed for use in such polymerizations are manganese compounds, such as those disclosed in McNelis, U.S. Pat. Nos. 3,220,979; Nakashio, 3,573,257; and Olander, 3,956,242; 3,972,851; 3,965,069; 4,054,553; and 4,075,174. The disclosures of all of the above-mentioned patents and publications are incorporated herein by reference.
Although the above-mentioned disclosures suggest carrying out the reactions in a self-precipitating environment, and the Olander patents specifically state that with basic manganese chelates the self-precipitating system can comprise a mixture of an aromatic hydrocarbon with sufficient methanol to cause the polymer to precipitate, in actual practice many catalysts are inhibited because of a reduction in efficiency attributed to the high alcohol content of the reaction medium. Moreover, a substantially water-immiscible alcohol (as distinguished from methanol) seems to be critical to provide a high percentage of polymer solids in the reaction medium and the highest possible reaction rates.
It has now been discovered that a solvent system comprising an aromatic hydrocarbon and a substantially water-immiscible alcohol will serve to self-precipitate polyphenylene oxides in filterable form from reaction mixtures containing a basic manganese hydroxy oxime chelate catalyst. No additional precipitation step is required in the process. The total isolation procedure provides considerable cost savings in terms of polymer clean-up and solvent recovery.
The catalyst employed herein operates surprisingly efficiently under conditions under which the polymer product precipitates by itself. For example, manganese bis(benzoin oxime) functions at or phenol(2,6-xylenol)/Mn ratio of approximately 500-1000, considerably superior to the catalysts described in the references above. Also, the manganese complexes, especially with 2-phenyl-2-hydroxy-butan-3-one oxime is operable at 20-25 percent solids.